Heh, by blind survey I obviously meant a survey where you don't tell the user which model he's using, but I suppose it's pretty funny to think of blindfolded people holding different Minis and being asked to guess which ones they are.
I think it's pretty uncommon in this day and age for people to frequently do stuff with a computer that takes a solid hour of compute time, or even 10 minutes. And for the people who ARE doing things for that long, they are likely taking breaks or doing something else while the computation is occurring and that extra minute of time probably doesn't make much difference to them.
Personally I frequently run a program that takes about 40 minutes. A lot of times I start the program and go do something else and come back after it's done, or I start doing something else with the computer as it's computing and it makes very little difference to me if it finishes in 38 minutes or 42 since I'm in the middle of something else. Many times I don't even notice it's done until a few minutes after it finishes anyway. So I will be buying the i7 Mini later this week since it DOES make a difference to me if it finishes in 40 minutes or 80 minutes, but the 2.3->2.6 upgrade is irrelevant to me unless maybe it cost $20 instead of $100.
Of course I can't speak for everyone, but at least for me personally and a lot of colleague "media freelancers", it's quite common to sit by the computer the whole day and multitask, where a seemingly small performance upgrade of 10% can do a lot over the course of a whole day. If this 10% direct performance boost would result in, say, a modest overall 5% increase in productivity over an 8 hour workday, that would mean you could do the same amount of work in 7.5 hours or get 30-40 minutes more work done in the same time.
I'm a freelance photographer, and usually need Lightroom (which scales well over many cores/threads, and uses up to 100% cpu) to run in the background, converting/developing jpgs for clients to choose from, while I'm working in Photoshop with a specific image. All the time I'm copying files to/from harddrives/ftps, running mail, twitter, chrome, spotify, ical, word, and some other minor apps. And I also work ~10 hours when I'm at the office, since I'm out actually taking the photographs other days. And I know a lot of people, not just photographers, work like this.
So, even though it might not be the most common way of using a computer, like you said, I'm just pointing out that there still is a big difference between how people work. And a not insignificant amount of people use it like I do.
So, again, for me -personally- the $100 upgrade definately is worth it. I would even pay $200, and another $200 for a GPU. But that's probably more just me...
I more than that wish they would upgrade the MP, but that's another story.